Catalytic hydrocyanation systems, particularly pertaining to the hydrocyanation of olefins, are known in the art. For example, liquid phase systems useful for the hydrocyanation of butadiene to form pentenenitriles (PN) are known in the art, e.g., U.S. Pat. No. 3,766,237. As used in that patent, and as will be used herein, the term "pentenenitrile" is intended to mean a cyanobutene. Likewise, "butenenitrile" means cyanopropene. The pentenenitriles so formed are further subjected to hydrocyanation and, in some cases isomerization, to form adiponitrile (ADN), a commercially important material in the manufacture of nylon. Bidentate phosphite ligands complexed to zero-valent nickel and platinum are known to be useful in the liquid phase hydrocyanation of butadiene, as described by Baker et al., J. Chem. Soc., Chem. Commun., 1991, pages 803-804.
The overwhelming majority of prior art processes for the hydrocyanation of butadiene are conducted in the liquid phase, with all attendant waste disposal problems. Previous approaches toward carrying out gas phase hydrocyanation of olefinic compounds have usually started with monoolefinic, not diolefinic, compounds and have given rise primarily to saturated products, which could not be further hydrocyanated. For example, Dutch Patent 6916495 teaches that pivalonitrile is prepared by reaction of HCN and isobutylene over Al.sub.2 O.sub.3 or SiO.sub.2 catalysts; U.S. Pat. No. 3,584,029 teaches that propionitrile is prepared by reaction of HCN with ethylene over catalysts containing Ni salts, H.sub.3 PO.sub.4 and Al.sub.2 O.sub.3 ; and U.S. Pat. No. 3,547,942 discloses the reaction of HCN and butadiene in the gas phase over a mixed metal catalyst containing copper chromite and activated copper chromite, which does yield a mixture of pentenenitriles, with 77-82% selectivities to 3-pentenenitrile and 4-pentenenitrile. However, the reaction of U.S. Pat. No. 3,547,942 also requires a co-feed of HCl.
Several patents teach that reaction of HCN with butadiene, ethylene, propylene or butenes, and additionally with air or oxygen in the gas phase, over various supported metal-containing catalysts give rise to cyanated olefinic products. However, in the olefinic products so produced the olefinic double bond is usually conjugated with the triple bond of the cyano group, and, therefore, substantially useless for the production of adiponitrile. For example, see:
U.S. Pat. No. 3,865,863, Asahi, Feb. 11, 1975 ##STR1##
U.S. Pat. No. 3,574,701, Asahi K. K. K., Apr. 13, 1971 ##STR2##
U.S. Pat. No. 3,578,695, Standard Oil, May 11, 1975 ##STR3##
U.S. Pat. No. 3,869,500, Asahi, Mar. 4, 1975 ##STR4##
The present invention provides a catalyzed gas phase process for the hydrocyanation of diolefinic compounds which is rapid, selective, and efficient. While certain solvents or diluents can be used in this process, they can be eliminated altogether. Furthermore, the catalyst is utilized as a stationary solid phase, which can reduce the costs of catalyst synthesis, recovery, and recycle, as well as the disposal cost of byproduct waste. A corollary benefit is the reduction of the cost of capital equipment needed for the process. Other objects and advantages of the present invention will become apparent to those skilled in the art upon reference to the detailed description of the invention which hereinafter follows.